ABSTRACT
When such a SiGe alloy layer is epitaxially grown on a substrate with a different lattice constant, for instance a Si-substrate, the growing layer will in first instance try to adapt its in-plane lattice constant as to form a coherent interface with the underlying substrate. The term pseudomorphic growth is often used for this type of growth. It can be easily understood that under these conditions a large elastic strain will be built in the commensurate layer. Equilibrium theories are needed to calculate the structure of stable epilayers. If the layers are metastable, strain relaxation by the introduction of dislocations occurs with aging or on heating the layers. The layers tend to approach the final equilibrium configuration. Equilibrium theories are also required to calculate the rate of strain relaxation in metastable layers. The improvement of the theories concerning critical thickness, equilibrium strain relaxation in layers exceeding the critical thickness and strain relaxation rate form the subject.
